Cover

ABSTRACT

A cover for a body, including at least one layer having a low emissivity coefficient for radiation associated with radiative heat loss from the body with wavelengths in a first frequency band.

TECHNICAL FIELD

The present invention provides a cover suitable for agricultural, industrial and commercial applications where a body needs to be protected from heat losses and/or be heated to maintain a desired temperature.

The present invention is particularly applicable to covers for swimming pools, and provides a pool cover which acts as an improved passive solar heating blanket.

In industrial applications, the solar heating ability of the cover reduces the heating input required from other means, such as electricity, resulting in a financial saving for the user, as well as having environmental benefits in reducing consumption of energy from less-sustainable sources. One example of an industrial application of the cover is to cover sewerage ponds.

In horticultural applications the cover could be applied to the soil to elevate and/or maintain soil temperature to encourage seed growth in early spring, or used over a frame to create a shelter for growing plants.

BACKGROUND ART

Any discussion of the prior art throughout the specification is not an admission that such prior art is widely known or forms part of the common general knowledge in the field.

Pool covers are placed over swimming pools (especially heated swimming pools) to reduce heat losses when the atmosphere is cooler than the temperature of the water in the pool. Heat can be lost from the surface of a swimming pool by evaporation, by radiation, and by convection when the air directly above the water's surface is heated, rises and carries the heat away, and is then replaced by colder air. By covering the surface of the water, heat losses by evaporation are reduced, and can be virtually eliminated.

A standard type of pool cover is fabricated from polyethylene (PE), and includes a single continuous primary sheet. A secondary sheet of PE is moulded to provide a plane with a series of protrusions. These protrusions are substantially cylindrical in shape, but rounded at the closed distal end of each protrusion. In one form each cylinder is approximately 5 mm in height, and has a diameter of about 18 mm. The plane of the secondary sheet is laminated to the primary sheet, so that the primary sheet closes off each protrusion to produce a series of air-filled bubbles. Standard pool covers are typically either semi-transparent blue or black.

This type of cover is placed on the surface of a water-filled pool with the bubbles on the lower side, and the primary sheet on the upper side. Air is trapped under the primary sheet in the spaces between the bubbles, aiding the buoyancy of the cover.

The continuity of the primary sheet isolates the surface of the pool from the atmosphere, limiting evaporative losses. The air-filled bubbles provide thermal insulation against conductive heat transfer from the surface of the water to the top of the pool cover. The temperature differential between the exposed surface and the atmosphere is therefore reduced, with a corresponding reduction in the amount of heat lost through the process of convection. This type of standard pool cover may typically reduce thermal loss by an average of 84% over an ambient temperature range of 0 to 25° C., compared with an uncovered pool.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a cover which achieves at least one of the following goals: to reduce heat losses from a body to atmosphere; to increase passive solar heating; or to provide the consumer with a useful choice.

The present invention provides a cover for a body, including at least one layer having a low emissivity coefficient for radiation associated with heat loss from the body with wavelengths in a first wavelength range, said first wavelength range having a minimum wavelength of 2500 nm; and wherein the cover has a high transmittance of radiation with wavelengths in a second wavelength range, said second wavelength range including the range 400 nm to 1100 nm.

The cover may include a layer having a low emissivity coefficient for radiation associated with heat loss from the body with wavelengths in the first frequency band made of a material selected from the group consisting of: polyvinylchloride (PVC), ethylene-vinyl-acetate (EVA) co-polymers, or appropriate compositions of polyethylene (PE). Alternatively a layer may include a thin film made of a material selected from the group consisting of: metal, metal oxides, PVC or polyvinylfluoride (PVF) films and other low-emissivity coatings. The base of the layer may be PE. The thin film may be applied by means such as spray-coating, vacuum deposition or evaporation coating, or by lamination or gluing, and may be 50 to 120 microns thick.

The second wavelength range may include the range 250 nm to 1100 nm, or 400 nm to 3000 nm, or 250 nm to 3000 nm.

In a first preferred embodiment, the cover includes a plurality of sealed cavities. These may be filled with a gas selected from the list consisting of: air, nitrogen, SF₆, argon, xenon or krypton.

In a second preferred embodiment, the cover includes a first layer, a second layer and a third layer, wherein the second layer is configured so that the cover includes a continuous matrix of sealed cavities between the first layer and the third layer.

Preferably the body is a body of fluid. The cover may include a fluid-repellent coating. This reduces “wetting” of the cover surface, and limits the ingress of fluid into spaces between the sealed cavities in the cover. In applications where the fluid is water, a side of the cover which is adjacent the body of water in use is treated with a hydrophobic coating.

At least one layer may be made of a substantially recycled material.

Preferably at least one layer is made of PE.

In a highly preferred form, the cover is a swimming pool cover.

BRIEF DESCRIPTION OF DRAWINGS

By way of example only, preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings, in which:

FIG. 1 shows a first preferred embodiment of a cover according to the present invention, when in use; and

FIG. 2 shows a second preferred embodiment of a cover according to the present invention, when in use.

FIRST PREFERRED EMBODIMENT

A first embodiment of a cover 101 according to the present invention is shown in FIG. 1 in situ over a body of fluid 102.

Cover 101 is constructed from two layers, laminated together. A first layer 103 is a planar sheet, and second layer 105 is a contoured PE layer of the type used in a standard pool cover to create the air-filled bubbles, including a plane, with a series of protrusions. In this first embodiment, these protrusions are substantially cylindrical in shape, but rounded at a closed distal end of each protrusion.

First layer 103 has a low emissivity coefficient for radiation in a first wavelength range, e.g. >2500 nm. This may be achieved by fabricating first layer 103 from an appropriate material such as PVC, EVA co-polymers, or appropriate compositions of PE. Alternatively the first layer may include a thin film having the appropriate qualities, such as a metal oxide or PVC or PVF film or other known low-emissivity coating. The thin film may be applied to a standard base, such as PE, by means such as spray-coating, vacuum deposition or evaporation coating, or by lamination or gluing, and may be 50 to 120 microns thick.

In this preferred embodiment, both first layer 103 and second layer 105 have a high transmittance of solar radiation in a second wavelength range, e.g. 250 nm-1100 nm, to maximise the available passive solar heating.

To construct the cover 101, first layer 103 is laminated to the plane of second layer 105, sealing off each protrusion to form a series of sealed, air-filled primary bubbles 106. Other shapes of protrusions may be used, to create alternative shapes of primary bubbles 106. The outer edges of the cover 101 are sealed. The exact shape and size of primary bubbles 106 may vary, depending on the shape and size of the protrusions in second layer 105. Primary bubbles 106 may be filled with alternative filling gases, such as nitrogen, SF₆, argon, xenon or krypton gas.

It has been found that in manufacturing the cover, that directly laminating a PVC first layer 103 to the second layer 105 can lead to a collapse in the primary bubbles 106, owing to the high temperature and pressure required for bonding PVC to PE.

In one preferred method, to overcome this problem and improve fabrication, a first layer 103 is pre-prepared as a sheet of PVC laminated to a thin layer of PE. The second layer 105 can then be bonded to the PE underside of the first layer 103 at a lower temperature, while maintaining the advantages of the cover including a first layer of PVC.

In another preferred method, the secondary layer 105 is bonded to a PE layer, and a layer of PVC is then laminated on to this PE layer, so that the PE layer and PVC layer together form first layer 103 of the finished cover 101.

When the fluid to be covered is water, the second layer 105 is preferably provided with a hydrophobic coating. This reduces wetting of the second layer 105 when the cover is in use, allowing for air to be trapped between the primary bubbles 106 and the surface of the fluid 102. This aids the buoyancy of the cover 101, as well as providing a barrier to the conduction of heat from the fluid 102 directly to the first layer 103, and thence to atmosphere.

Cover 101 is placed over the surface of the body of fluid 102 with the first layer 103 on the upper-most side, exposed to the atmosphere. Solar radiation A in the second wavelength range can pass through the first layer 103 and the primary bubbles 106 to enter the fluid 102. Solar radiation A imparts energy to the body of fluid 102 in the form of heat.

Maximum heating of the body of fluid 102 by solar radiation A is achieved by the high transmissivity of the cover 101 to solar radiation in the second wavelength range. This reduces both the reflectivity of the upper surface of the cover 101, and also the amount of heat absorbed by the cover 101 itself. In the past, it had been believed that a black cover would provide superior heating, because it absorbs more solar radiation. However, a heated cover will only transfer this heat by conduction to the fluid immediately adjacent the cover. Therefore, unless there is significant agitation of the fluid 102 there is no benefit to heating the cover 101. By contrast, the optically transparent cover of the present invention allows radiation, e.g. solar radiation, to penetrate into the body of fluid, providing for more even and effective heating.

First layer 103 reduces the heat lost through radiation, and preferably includes a PVC film. When longer wavelength infra-red heat radiation B in the first wavelength range leaves the body of fluid 102, it can pass through the primary bubbles 106. However, when it encounters first layer 103, at least some of heat radiation B is reflected back to the fluid 102. It has been found that the inclusion of a PVC sheet improves the reduction in thermal loss, when compared to a cover made solely of PE.

The improved cover 101 promotes passive solar heating of the fluid 102 by maximising the energy which enters the fluid 102 in the form of solar radiation, and traps the heat by minimising evaporation and radiation losses as described above.

The high transmittance of the cover 101 to radiation in the first wavelength range allows approximately 77% of incident solar radiation in the range 200 to 1100 nm to enter the body of fluid 102 by transmission through the cover, compared with a standard blue tinted PE pool cover, which generally only transmits 64% of incident solar radiation in the same range. This improves the passive solar heating of a body of fluid covered by the cover of the present invention.

By combining an improved ability to reduce radiative heat loss with an increased allowance for solar heating of the body of fluid, the present invention provides a cover which acts as a passive solar blanket, providing in optimal conditions for a net gain in the fluid temperature, compared with an uncovered body of fluid. When applied to a swimming pool cover, this allows for extension of the comfortable swimming season, particularly in temperate climates. This cover also potentially reduces the electricity consumption required for active heating, and, where present, any associated CO₂ emissions.

SECOND PREFERRED EMBODIMENT

A cover 201 according to the present invention is shown in FIG. 2 in situ over a body of fluid 202.

Cover 201 is constructed from three layers, laminated together. A third layer 203 is a planar sheet of PE, and a first layer 204 is a planar sheet, fabricated as described below. Second layer 205 is a contoured PE layer of the type used in a standard pool cover to create the air-filled bubbles, including a plane, with a series of protrusions. In a preferred embodiment, these protrusions are substantially cylindrical in shape, but rounded at the closed distal end of each protrusion.

First layer 204 has a low emissivity coefficient for radiation in a first wavelength range, e.g. >2500 nm. This may be achieved by fabricating first layer 204 from an appropriate material such as PVC, EVA co-polymers, or appropriate compositions of PE. Alternatively the first layer may include a thin film having the appropriate qualities, such as a metal oxide or PVC or PVF film or other known low-emissivity coating. The thin film may be applied to a standard base, such as PE, by means such as spray-coating or evaporation coating, or by lamination or gluing, and may be 50 to 120 microns thick.

In this preferred embodiment, all three layers have a high transmittance of solar radiation in a second wavelength range of the desired wavelengths of 250 nm-1100 nm, to maximise the available passive solar heating.

To construct cover 201, third layer 203 is laminated to the plane of second layer 205, sealing off each protrusion to form a series of sealed, air-filled primary bubbles 206. Other shapes of protrusions may be used, to create alternative shapes of primary bubbles 206. First layer 204 is laminated to the distal ends of the protrusions, closing off the spaces between primary bubbles 206 to create at least one secondary bubble 207. The outer edges of the cover 201 are sealed, so that primary bubbles 206 and secondary bubbles 207 form a continuous matrix of sealed cavities between the first layer 204 and the third layer 203. The exact shape of primary bubbles 206 and secondary bubbles 207 may vary, depending on the shape and size of the protrusions in second layer 205, for example, to give primary bubbles 206 and secondary bubbles 207 interlocking shapes of similar size. Primary bubbles 206 and/or secondary bubbles 207 may be filled with alternative filling gases, such as nitrogen, SF₆, argon, xenon or krypton gas.

It has been found that in manufacturing the cover, that directly laminating a PVC first layer 204 to the distal ends of the PE protrusions forming primary bubbles 206 can lead to a collapse in the primary bubbles 206, owing to the high temperature and pressure required for bonding PVC to PE.

In one preferred method, to overcome this problem and improve fabrication, a first layer 204 is pre-prepared as a sheet of PVC laminated to a thin layer of PE. The distal ends of the protrusions can then be bonded to the PE underside of the first layer 204 at a lower temperature, while maintaining the advantages of the cover including a first layer of PVC.

In another preferred method, the distal ends of the protrusions are bonded to a PE layer, to form the at least one secondary bubble 207. A layer of PVC is then laminated on to this PE layer, so that the PE layer and PVC layer together form first layer 204 of the finished cover 201.

Cover 201 is placed over the surface of the body of fluid 202 with first layer 204 on the upper-most side, exposed to the atmosphere. Solar radiation A in the second wavelength range can pass through first layer 204, primary bubbles 206 or secondary bubbles 207, and third layer 203, to enter the fluid 202. Solar radiation A imparts energy to the body of fluid 202 in the form of heat.

Maximum heating of the body of fluid 202 by solar radiation A is achieved due to the high transmissivity of the cover 201 of solar radiation in the second wavelength range. This reduces both the reflectivity of the upper surface of the cover 201, and also the amount of heat absorbed by the cover 201 itself. In the past, it had been believed that a black cover would provide superior heating, because it absorbs more solar radiation. However, a heated cover will only transfer this heat by conduction to the fluid immediately adjacent the cover. Therefore, unless there is significant agitation of the fluid 202 there is no benefit to heating the cover 201. By contrast, the optically transparent cover of the present invention allows solar radiation to penetrate into the body of fluid 202, providing for more even and effective heating.

One unique feature of the cover 201 is that the space between third layer 203 and first layer 204 comprises a continuous matrix of sealed bubbles, consisting of primary bubbles 206 and secondary bubbles 207. This reduces the conduction of heat through the cover 201 when compared to the prior art, and therefore reduces heat loss from the fluid 202. It is believed this feature provides an average thermal loss reduction of 89% over a 0 to 25° C. ambient temperature range, compared with 84% for the prior art.

First layer 204 reduces the heat lost through radiation, and preferably includes a PVC film. When infra-red heat radiation B in the first wavelength range leaves the body of fluid 202, it can pass through third layer 203 and the primary bubbles 206 or secondary bubbles 207. However, when it encounters first layer 204, at least some of heat radiation B is reflected back to the body of fluid 202. It has been found that the inclusion of a PVC sheet improves the reduction in thermal loss, when compared to a cover made solely of PE.

The improved cover 201 promotes passive solar heating of the body of fluid 202 by maximising the energy which enters the body of fluid 202 in the form of solar radiation, and trapping the heat by preventing evaporation, and reducing convection and radiation losses as described above.

It is believed that the pool cover of the present invention may reduce the average thermal loss by up to 97.4%, compared with an uncovered body of fluid. This represents an average 16% improvement over the prior art. Over an ambient temperature range of 0-25° C., the improvement in heat retention compared with the prior art is 26.7% to 0.5%, with the advantage over the prior art being greatest at low temperatures (0 to 10° C.). In addition, the optical transparency of the pool cover of the present invention may allow approximately 77% of incident solar radiation (in the range 200 to 1100 nm) to enter the body by transmission through the pool cover, compared with a standard blue tinted PE pool cover, which may only transmit 64% of incident solar radiation in the same range. This improves the passive solar heating of a body covered by the cover of the present invention.

By combining an improved ability to reduce heat loss with an increased allowance for solar heating of the body, the present invention provides a cover which acts as a passive solar blanket, providing in optimal conditions for a net gain in the fluid temperature, compared to an uncovered body. This net heat gain may be 47.6% higher than the net gain of a body covered by a prior art pool cover. When the body is a swimming pool, this should allow for extension of the comfortable swimming season, particularly in temperate climates. This cover also has the potential to reduce the electricity consumption required for active water heating, and, where present, any associated CO₂ emissions.

Third layer 203 provides a smooth lower surface for cover 201, making it easier to clean than a pool cover according to the prior art, and reducing the available habitat for bacterial growth. 

1. A cover for a body, including at least one layer having a low emissivity coefficient for radiation associated with radiative heat loss from the body with wavelengths in a first frequency band.
 2. The cover according to claim 1, wherein the first frequency band has a minimum wavelength of 2500 nm.
 3. The cover according to either one of the preceding claims, wherein a layer having a low emissivity coefficient for radiation associated with radiative heat loss from the body with wavelengths in the first frequency band is made of a material selected from the group consisting of: PVC, EVA co-polymers and appropriate compositions of PE.
 4. The cover according to either one of claim 1 or 2, wherein a layer having a low emissivity coefficient for radiation associated with radiative heat loss from the body with wavelengths in the first frequency band includes a thin film made of a material selected from the group consisting of: metals, metal oxides, PVC, PVF films and other low-emissivity coatings.
 5. The cover according to claim 4, wherein the thin film is applied to a base layer made of PE.
 6. The cover according to claim 1, wherein the cover has a high transmittance of radiation with wavelengths in a second frequency band.
 7. The cover according to claim 6, wherein the second frequency band is 250 nm to 3000 nm.
 8. The cover according to claim 7, wherein the second frequency band is 400 nm to 3000 nm.
 9. The cover according to any one of the preceding claims, which includes a plurality of sealed cavities.
 10. The cover according to claim 9, wherein the sealed cavities are filled with a gas selected from the list consisting of: air, nitrogen, SF₆, argon, xenon or krypton.
 11. The cover according to either one of claim 9 or 10, including a first layer, a second layer and a third layer, wherein the second layer is configured so that the cover includes a continuous matrix of sealed cavities between the first layer and the third layer.
 12. The cover according to any one of the preceding claims, including at least one layer made of PE.
 13. The cover according to any one of the preceding claims, wherein the body is a body of fluid.
 14. The cover according to claim 13, including a fluid-repellent coating.
 15. The cover according to either one of claim 13 or 14, wherein the body of fluid is a swimming pool. 